As is well known to participants of aquamarine activities (e.g. surfboard operator, water-ski operator, etc.) an elongate rope-like tether has its trailward-end attached to a girdle encirling the operator's arm, leg, or waist, and has its leadward-end attached to a water-borne tow (e.g. surfboard, motorboat tow for water-ski, etc.). Because of the velocity and/or sinuous path of the water-borne tow, the operator of the surfboard, water-ski, etc., can be subjected to a perilous condition e.g. wherein the tether begins to wrap about the operator's body. Such tether wrapping can cause severe injury, or even drowning. Prior workers in the aquamarine sports art have attempted to provided lockably-releasable tethering devices intended: to provide secure engagement between the tether and the operator's body girdle; but to enable the operator (somehow discerning a perilous condition) to quickly and reliably manually disengage the tether trailward-end from the body girdle. However, such attempts heretofore by prior art workers have been marginally acceptable, at best.